The invention relates to an optical communication module for optical signal transmission, and more particularly to an optical communication module having a structure adopting folding at a filter and a process for producing the same.
A conventional optical communication module having a structure adopting folding at a filter is disclosed, for example, in Japanese Patent Laid-Open No. 068705/1999. This module is shown in FIG. 1.
Japanese Patent Laid-Open No. 068705/1999 proposes that, in the optical communication module utilizing two-way WDM (wavelength division multiplexing), a groove is provided in a silicon substrate and a dielectric multilayer film filter is inserted into the groove with a view to reducing crosstalk light, which has leaked from LD (laser diode) light into PD (photodiode) light, to a level such that poses no practical problem.
FIG. 2 shows another prior art technique disclosed in Japanese Patent Laid-Open No. 352341/1999.
This Japanese Patent Laid-Open No. 352341/1999 proposes that, in a wavelength multiplexing optical communication module, in order to realize good receive characteristics, a cross portion, which crosses a first optical waveguide and a second optical waveguide each other at the end face of an optical waveguide substrate is provided and, in addition, a filter, which reflects light with wavelength xcex1 and permits transmission of light with wavelength xcex2, is provided at the end face of the optical waveguide substrate.
In these optical communication modules, the structure utilizing folding at a filter can reduce crosstalk light, i.e., light that has leaked from LD light into PD light, to a level which poses no practical problem.
In assembling the above optical communication modules, however, the optical axis of the optical fiber and the optical waveguide should be regulated while monitoring output light, and the troublesome assembling work disadvantageously incurs high assembly cost.
In order to solve this problem of the prior art, a method has been proposed wherein a V groove for a fiber guide is provided in an optical waveguide substrate to facilitate the regulation of the optical axis of the optical fiber and the optical waveguide.
The use of the V groove in the regulation of the optical axis of the optical fiber and the optical waveguide can realize the registration of the optical fiber without the regulation of the optical axis which in turn realizes a reduced assembly cost.
The V groove is generally prepared by removing the (100) crystal face of a wafer by anisotropic etching to form a V-shaped groove of (111) crystal face. Therefore, the direction of the V groove is determined by the axial direction of the wafer crystal.
FIG. 3 is an example of crystal axial direction ( less than 110 greater than axial direction) and mask direction of a wafer 90g in the preparation of a conventional optical waveguide substrate 10.
A V groove 13 in the optical waveguide substrate 10 is formed by removing the (100) crystal face of the wafer 90 by anisotropic etching to form a V-shaped groove having (111) crystal face.
In the conventional production method of a V groove, as shown in FIG. 3, positioning is carried out so that the direction of a mask for preparing a pattern of the optical waveguide substrate 10 is parallel to the crystal axial direction of the wafer 90.
In the same manner as described in the conventional optical communication modules shown in FIGS. 1 and 2, a bent waveguide is used to apply, in the inside of the optical waveguide substrate, an optical signal diagonally to the filter provide perpendicularly to the V groove to perform reflection or transmission of the optical signal.
As described above, the conventional optical communication modules had the following problems.
First, in assembling an optical communication module having a structure adopting folding at a filter, the optical axis of the optical fiber and the optical waveguide should be regulated while monitoring output light, and this work disadvantageously incurs high assembly cost.
Second, in the inside of the optical waveguide substrate, an optical signal is applied diagonally to a filter. This necessitates a bent waveguide.
In the conventional production process of an optical communication module, as shown in FIG. 3, the optical waveguide substrate 10 is masked parallel to the crystal axial direction of the wafer, and, in addition, a filter is provided perpendicularly to the center line of the optical waveguide substrate 10. For this reason, the direction of the V groove 13 formed by anisotropic etching becomes perpendicular to the filter, and a bent waveguide is necessary for diagonally applying the optical signal.
When the waveguide is not straight but has a bend, the optical signal loss occurs. In order to reduce this loss, the radius of curvature of the bent waveguide should be larger than a given dimension. For this reason, a certain length is necessary for the optical waveguide. This makes it impossible to reduce the size of the optical waveguide substrate.
Since the size of the optical waveguide substrate cannot be reduced, the size of the optical communication module cannot also be reduced. For this reason, the production cost of optical communication modules has hitherto been high.
Accordingly, it is a first object of the invention to solve the above problems of the prior art and to provide an optical communication module, which has a small size and a low production cost and is suitable for mass production, and a process for producing the same.
It is a second object of the invention to solve the above problems of the prior art and to provide an optical communication module, which, through the realization of the formation of a V groove for fiber guide diagonally to a filter, can render a bent waveguide unnecessary and can construct the waveguide by a straight waveguide only to realize a reduction in size of the optical waveguide substrate, and a process for producing the same.
According to the first feature of the invention, an optical communication module for optical signal communication, comprises:
a filter for transmission and reflection of the optical signal;
an optical fiber; and
a straight waveguide provided, between the filter and the optical fiber, as a waveguide for communication of the optical signal.
Preferably, a groove for installing the optical fiber is linearly provided, from the end of the waveguide, in the same direction as and parallel to the direction of the optical fiber.
Preferably, a first optical waveguide and a second optical waveguide are provided as the straight waveguide for optical signal communication, the first optical waveguide and the second optical waveguide are provided at respective angles such that an optical signal introduced from the first optical waveguide is reflected from the filter and transmitted to the second optical waveguide and one end of each of the first and second optical waveguides is disposed at a position close to the optical signal reflection point in the filter, and a groove for installing the optical fiber is disposed straightly relative to and in the same direction as the second optical waveguide so as to extend from the end of the second optical waveguide remote from the filter toward the opposite direction of the second optical waveguide.
Preferably, the optical communication module further comprises a receive photodetector for receiving a receive optical signal, and a light-emitting device for sending a send optical signal. In this case, preferably, the first optical waveguide receives the send optical signal sent from the light-emitting device and then sends the optical signal to the filter, the second optical waveguide receives the send optical signal sent through the first optical waveguide and reflected from the filter and sends the optical signal to the optical fiber provided in the groove, and, further, receives the receive optical signal sent through the optical fiber and sends the optical signal to the filter, and the receive photodetector receives the receive optical signal which has been sent from the second optical waveguide and has passed through the filter.
A third waveguide for communication of the receive optical signal may be provided between the filter and the receive photodetector.
In this case, a monitoring photodetector for monitoring the output of the photodetector may be provided behind the light-emitting device.
In the optical communication module according to the first feature of the invention, preferably, the receive optical signal is different from the send optical signal in wavelength, and the filter permits the transmission of the receive optical signal and reflects the send optical signal to perform two-way communication of wavelength division multiplexing.
Preferably, the receive optical signal and the send optical signal are identical to each other in optical signal wavelength, and the filter partially reflects light with the wavelength of the receive optical signal and light with the wavelength of the send optical signal and permits the transmission of a part of these lights to perform two-way communication using optical signals with an identical wavelength.
Preferably, the receive optical signal and the send optical signal are identical to each other in optical signal wavelength, and the filter has a half mirror, for partially reflecting light with the wavelength of the receive optical signal and light with the wavelength of the send optical signal, and permitting the transmission of a part of these lights, and a filter film which permits the transmission of light with the wavelength of the receive optical signal and light with the wavelength of the send optical signal and does not permit the transmission of light with wavelength of input noise light, and the input noise light is cut off to perform two-way communication using optical signals with an identical wavelength.
Preferably, parts in each section for two-way communication are constructed on a chip of the optical waveguide substrate.
Preferably, the groove for installing the optical fiber is formed on the optical waveguide substrate.
Preferably, the groove for installing the optical fiber is formed in a V form in section by anisotropic etching in the optical waveguide substrate.
Preferably, the optical waveguide substrate is in the form of a parallelogram of which the angle of the vertex is not right angle, and the groove and the filter are provided parallel respectively to adjacent two sides of the parallelogram in the optical waveguide substrate.
Preferably, a carrier for mounting the receive photodetector for receiving the receive optical signal is provided and the receive photodetector is mounted within the carrier, which is installed, rather than within the optical waveguide substrate, at a position that receives the receive optical signal which has passed through the filter.
According to a second feature of the invention, an optical communication apparatus provided with an optical communication module for optical signal communication is provided wherein the waveguide for communication of the optical signal provided between the filter for the transmission and reflection of the optical signal and the optical fiber within the optical communication module is a straight waveguide.
Preferably, a groove for installing the optical fiber is linearly provided within the optical communication module, from the end of the waveguide, in the same direction as and parallel to the direction of the optical fiber.
Preferably, a first optical waveguide and a second optical waveguide are provided as the straight waveguide for optical signal communication within the optical communication module, the first optical waveguide and the second optical waveguide are provided at respective angles such that an optical signal introduced from the first optical waveguide is reflected from the filter and transmitted to the second optical waveguide and one end of each of the first and second optical waveguides is disposed at a position close to the optical signal reflection point in the filter, and a groove for installing the optical fiber is disposed straightly relative to and in the same direction as the second optical waveguide so as to extend from the end of the second optical waveguide remote from the filter toward the opposite direction of the second optical waveguide.
According to the third feature of the invention, a process for producing an optical communication module for optical signal communication is provided, wherein a straight waveguide is linearly formed as a waveguide for communication of the optical signal provided between an optical fiber and a filter for the transmission and reflection of an optical signal.
In the production process, preferably, a groove for installing the optical fiber is linearly provided, from the end of the waveguide, in the same direction as and parallel to the direction of the optical fiber.
In the production process, preferably, a first optical waveguide and a second optical waveguide are provided as a straight waveguide for optical signal communication, the first optical waveguide and the second optical waveguide are provided at respective angles such that an optical signal introduced from the first optical waveguide is reflected from the filter and transmitted to the second optical waveguide and one end of each of the first and second optical waveguides is disposed at a position close to the optical signal reflection point in the filter, and a groove for installing the optical fiber is disposed straightly relative to and in the same direction as the second optical waveguide so as to extend from the end of the second optical waveguide remote from the filter toward the opposite direction of the second optical waveguide.
In the production process, preferably, parts in each section for two-way communication are constructed on a chip of the optical waveguide substrate.
In the production process, preferably, the groove for installing the optical fiber is formed on the optical waveguide substrate by anisotropic etching.
In the production process, preferably, the groove for installing the optical fiber is formed in a V form as viewed in section on the optical waveguide substrate.
In the production process, preferably, a mask for forming each chip of the optical waveguide substrate is formed on a wafer diagonally relative to the axial direction of the wafer crystal.
In the production process, preferably, a mask for each chip of the optical waveguide substrate is formed on a wafer in the longitudinal direction along the crystal face orientation of the wafer and in the lateral direction diagonally relative to the crystal face orientation of the wafer and the optical waveguide substrate is formed in a parallelogram form.
In the production process, preferably, a groove for the insertion of the filter and a groove for abutting against the optical fiber provided in each of the optical waveguide substrates are formed at a time for each line of the optical waveguide substrates in the mask of the wafer.